Conventional rotary power is designed to be used as it is generated, with direct linkages and gears. Some applications, such as automobile engines, require a energy/momentum storage device that links the power generation and power consumption stages of the engine system.
The automobile engine and transmission system possesses a cylindrical flywheel which is literally a metal wheel. Setting this flywheel spinning stores a certain amount of energy and momentum in the wheel's motion, which can be used when the transmission is engaged by means of a clutch.
Other power generation systems, such as turbines and windmills also benefit from flywheel application, to minimize power interruptions and smooth out power flows. The shape of “flywheels” is based on the stored angular momentum of a spinning, flat cylinder with an axis of rotation through its center. Alternative spinning shapes can be used to store angular momentum and mechanical energy as well.